A. Field of the Invention
The present invention relates to a multizone air conditioning system having a plurality of individual evaporator units and more particularly to a system and evaporator units which provide a balanced charge of refrigerant in the system, regardless of whether individual units are activated or deactivated at a given time.
B. Description of the Prior Art
Multizone air conditioning and heat pump systems have been used to provide individual heating or cooling to separate zones within the system. Such systems typically include a single outdoor compressor and a plurality of individual evaporator units, which cool or heat the zones in which they are located. Examples of such systems are described in U.S. Pat. Nos. 2,978,877 to Long; 3,797,265 to Garland; 4,620,423 to Hopkinson et al.; 4,643,002 to Dennis et al.; and 4,760,707 to Dennis et al.
The use of multizone systems is becoming popular where it is desirable to control the environment in individual rooms such as in residential and light commercial applications. In such systems, fewer than all of the evaporator units and associated fans in the individual rooms may be in active operation at any given time. When less than all evaporator units are active, the system will become unbalanced both in terms of capacity of the outdoor and indoor units, and in terms of the refrigerant in the system.
Many of these systems, such as the system disclosed in Long, Garland, and Dennis et al., require use of complex bleed-off systems, holding tanks, or accumulators to attempt to balance the refrigerant charge within the multizone system. For example, the recently issued '707 to Dennis et al. explains that one approach to solve these problems is to provide bleed-off valves between the high and low sides of the system. Such bleed-off valves are opened to allow a portion of the liquid refrigerant to flash over to the low pressure side. Dennis et al. discloses the use of a bleedoff valve 81 and also includes a thermocharger 82 with associated temperature sensor and check valves to subcool liquid refrigerant passing through a heat exchanger in the thermocharger 82, to thereby increase the efficiency of the system. Dennis et al. also includes an accumulator 34 to hold refrigerant.
The complex systems disclosed in the prior art add appreciably to the costs of the systems. The complexity also often results in a decrease in the efficiency of the system.